The present invention relates to a substrate holder, a stage apparatus, and an exposure apparatus, and more particularly relates to, for example, a substrate holder and a stage apparatus that are ideal for vacuum chucking a substrate, such as a wafer, as well as an exposure apparatus that comprises this substrate holder.
The disclosure of the following priority application is hereby incorporated by reference in its entirety: Japanese Patent Application No. 2004-253978, which was filed on Sep. 1, 2004.
Projection type exposure apparatuses and laser repair apparatuses are known examples of apparatuses that fabricate, for example, semiconductor wafers (hereinbelow, called wafers) used in the manufacture of semiconductor devices as well as substrates, such as glass substrates.
In the case of a projection type exposure apparatus, a projection lens (projection optical system) is provided for imaging and projecting a circuit pattern of a reticle onto a substrate front surface at a prescribed magnification. This projection lens needs to have high resolving power, particularly in the case of a reduction projection lens, while simultaneously securing a large projection area, and, consequently, the NA (numerical aperture) has increased year by year while the depth of focus has attendantly decreased.
Consequently, with an exposure apparatus as described above, the substrate must be precisely planar in order to prevent resolution defects that are caused by the mispositioning of the substrate front surface with respect to the focal point position, and thereby to form a fine circuit pattern; therefore, a substrate holder is used that vacuum chucks the abovementioned substrate and performs a correction to flatten the substrate within a prescribed plane.
Patent Document 1 cites an example of a prior art substrate holder wherein support pins are provided that support a wafer inside a suction chamber that is surrounded by part covers the outer circumferential wall of a wafer chuck (substrate holder), which vacuum chucks the wafer by negatively pressurizing the suction chamber in a state wherein the wafer is chucked and flat with respect to the upper surfaces of the support pins and the outer circumferential wall. In addition, with this type of substrate holder, the suction force applied by the suction apparatus to negatively pressurize the suction chamber acts upon the inner flat surface of the wafer, but not upon its outer circumferential part, which causes such to warp even when using a wafer that has satisfactory flatness.
Accordingly, Patent Document 1 discloses a technology that employs the Venturi effect to cause a force to act in a direction that prevents warpage of the wafer's outer circumferential part by providing a suction groove, which externally draws a gas into the suction chamber, to the outer circumferential wall.
Nevertheless, the related art discussed above has the following types of problems.
When forming the suction groove in the outer circumferential wall, there is a problem in that it is necessary to strictly control the size of the suction groove in order to control the force that prevents warpage, which makes alignment troublesome.
In addition, there is also a concern that when liquid is filled between the wafer and the projection optical system and a pattern is exposed on the wafer through this liquid, i.e., when so-called immersion exposure is performed, the liquid will infiltrate the suction chamber from the suction groove.
In addition, to reduce the effect of dust located between the wafer and the support pins, the size of the upper surfaces of the support pins have shrunk in recent years, thereby creating a tendency for the support pin tips to bite into the rear surface of the wafer, which in turn tends to increase warpage (waviness) of the wafer between the location of the wafer that is supported by the outer circumferential wall and the location that is supported by the support pins.
Waviness of an exposure slit (a slit through which exposure illumination light is projected), which is for transferring the pattern to the wafer, is compensated for by correcting the position of the wafer front surface by driving (e.g., leveling) a wafer stage so that the flatness of the slit is within a prescribed value; however, compensating for waviness using the stage drive is problematic because, for example, waviness increases if the exposure slit is at a position where it straddles the outer circumferential wall.
A purpose of some aspects of the invention is to provide a substrate holder that can hold a substrate so that its flatness is stable and satisfactory even at a circumferential edge part that surrounds a suction space, as well as a stage apparatus and an exposure apparatus.